Friction dampener particularly adapted to railway vehicle motion control

ABSTRACT

A friction dampener can include a housing having one end slidably surrounding one end of a shaft movable relative thereto. Opposing ends of the housing and shaft can each having a connecting eye member for connection to separate independently movable elements. One or more friction elements can be carried by the shaft which frictionally engage inner surfaces of the housing. The friction elements can have inner and outer portions having different material properties. The housing can be adapted to generally maintain the pressure between the friction elements and the housing within a range of desirable pressures.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of Ser. No. 09/257,445 filed Feb. 25,1999, now U.S. Pat. No. 6,279,693 based on Provisional PatentApplication Ser. No. 60/076,044, filed Feb. 26, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to energy (shock) absorbing devices, andmore particularly to a friction dampener adapted to railway vehiclemotion control.

2. Description of the Prior Art

Various types of shock absorption and dampening devices have beenemployed for many years in a variety of different applications. The mostprevalent of such devices is probably the shock absorber, which isfrequently used in a variety of different kinds of vehicles. The mostcommon type of shock absorber is probably the hydraulic shock absorber,which utilizes a fluid filled cylinder and a plunger mechanism.Typically, the cylinder housing and the plunger are separatelyconnectable to external elements which are expected to undergo relativedisplacements. However, there can be many applications where an energyabsorber is called for, but where the hydraulic shock absorber is notnecessarily desirable for many possible reasons. For example, modernhydraulic shock absorbers are relatively complex, expensive, and can bemuch heavier than friction type dampening devices. Furthermore, becauseof the fluid medium utilized in hydraulic shock absorbers, theorientation of such shock absorbers can have an effect on performance.For example, hydraulic shock absorbers are generally more efficient whenmounted in a relatively vertical orientation. Yet, there can be manyapplications where it is desirable to mount a shock absorber in ahorizontal orientation. In particular, one such application is where ashock absorber, or dampener, is utilized as a yaw dampener on a railwayvehicle truck assembly to control hunting.

Friction type shock absorbing devices, such as a friction dampener, canbe simpler in design, less expensive, lighter weight, and unaffected bythe orientation in which it is mounted. Various types of frictiondampeners have been employed in the past to provide shock absorption orcushioning features where the use of hydraulic shock absorbers wasundesirable. Prior friction dampeners can be one or two way energyabsorbers and commonly comprise a first member, such as a cylindricalhousing, a second member such as a shaft or rod, which is coaxiallydisposed within the housing, and a friction pad assembly carried by theshaft in sliding engagement with the inside surface of the housing. Boththe housing and the shaft or rod are provided with a connecting memberfor attachment to external elements which are expected to undergorelative displacement. Such a friction pad assembly generally includes afriction element and some type of wedge member to initially set (orreset) the pressure between the friction element and the inside surfaceof the housing. Two examples of such friction dampeners are disclosed inU.S. Pat. No. 3,866, 67,724 and U.S. Pat. No. 3,796,288, both toHolnick. The friction dampener disclosed in both of the aforementionedpatents provide a manual adjustment means for moving a wedge shapedmember between, or out from between, the friction element in order toincrease or decrease the force applied to the friction element againstthe inside surface of the housing.

Other friction dampeners have provided a leaf spring to bias thefriction element against the housing. One such device is disclosed inU.S. Pat. No. 3,121,218 to Hallinan. Such a device can have a leafspring that is bimetallic and manually adjustable to either urge thefriction element against the housing to increase the frictionalengagement, or reduce such pressure to decrease friction.

Still other friction dampeners have provided for a small servo motor toautomatically adjust the wedge member to increase or decrease thepressure between the friction element and the inside surface of thehousing. One such device disclosed in U.S. Pat. No. 5,080,204 to Boweret al. discloses a friction dampener for the drum of a washing machineunit. In Bower, a small servo motor is provided inside the dampener tooperate a piston which moves the wedge member in order to decrease thepressure between the friction element and the inside surface of thehousing. The servo motor is a thermoactuator element that is responsiveto a rotational speed sensor which triggers the servo motor when apredetermined rotational speed has been exceeded.

However, such friction dampener devices can be associated with certaindisadvantages resulting from the nature of the friction element whensuch devices are employed in some heavy load applications. An example ofsuch an application is the use of a friction dampener on a railwayvehicle truck assembly to control hunting, as referred to previously,wherein the truck assemblies can be carrying hundreds of tons ofmaterials. During operation of a friction dampener in such anapplication, the extremely large forces which the dampener must controlcan result in very high temperatures being generated by the frictionalinteraction between the housing and the friction element. Because thefriction element typically expands in response to an increase intemperature, this can causes a corresponding increase in the peripheralpressure on the housing. As might be expected, this increase inperipheral pressure normally results in causing the dampener to becomeincreasingly stiffer. Compounding the situation further, the frictioncoefficient of the friction element is typically sensitive totemperature. Thus, as the temperature increases the friction coefficientof the friction element usually also increases. This is analogous to thesituation where race car drivers spin the tires on the car to get thetire temperature up so they stick to the track better and resistslipping. A rubber/elastomeric compound experiencing this condition iscommonly referred to as being “tacky.” Thus, like the race car tires,the friction element can resist sliding on the inside surface of thehousing as the temperature increases. The result can be that duringoperation of the friction dampener the pressure becomes so great and thefriction element becomes so tacky that essentially no relative movementcan occur between the friction element and the housing in the normaloperating range. Basically the friction dampener can “lock up,” at whichpoint the dampener begins to behave like a fixed rod. This veryundesirable condition can result in damage to the friction dampener orthe externally connected elements which are expected to be able to moverelative to each other. Furthermore, since the yaw forces are not beingdampened, hunting of the truck assembly can get out of control.

Therefore, friction dampeners which do not provide some means forcontrolling the peripheral pressure between the friction element and thehousing can be unacceptable in certain applications where the frictiondampener must control heavy loads and undergo large variations intemperature and pressures. Accordingly, there is a need for a frictiondampener which can generally maintain the peripheral pressure betweenthe friction element and the housing within a preferred range ofacceptable operating pressures.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a frictiondampener which can generally maintain the peripheral pressure betweenthe friction element and the housing within a certain preferred range ofacceptable operating pressures. The friction dampener can be mounted inany orientation without loss of performance, can be lighter in weightand less expensive to manufacture than a typical hydraulic shockabsorber.

Such a friction dampener can include a housing having one end slidablysurrounding one end of a shaft movable relative thereto. Opposing endsof the housing and shaft can each having a connecting eye member forconnection to separate independently movable elements. One or morefriction elements can be carried by the shaft which frictionally engageinner surfaces of the housing. The friction elements can have inner andouter portions having different material properties. The housing can beadapted to generally maintain the pressure between the friction elementsand the housing within a range of desirable pressures.

In one embodiment, the friction dampener can have a generallycylindrical housing slidably surrounding a tubular shaft or rod.Friction element can be attached to the shaft for frictionally engagingan inside surface of the housing. More than one friction element may beattached to the rod and each friction element can have an annular,“donut,” shape. Each friction element can also have distinct inner andouter portions which are made of different compositions and havedifferent properties. The means for generally maintaining the peripheralpressure between each friction element and the generally cylindricalhousing within a preferred range of acceptable operating pressures canbe integral with the housing such that the housing is self-adjusting.This may accomplished by configuring the housing in such a manner as topermit the housing to expand in a controlled manner in response toincreased peripheral pressure. Thus, the expansion of the frictionelements, which can occur due to the build up of heat during operationof the device, can be compensated for by the self-adjusting housing togenerally maintain the peripheral pressure within a preferred range ofpressure.

In another embodiment, the friction dampener can be very similar to thefriction dampener described above, except having a generally rectangularhousing in which a generally rectangular shaft is slidably enclosed.Similarly to the generally cylindrical shaped dampener, the frictionelements are attached to the rectangular shaft for frictionally engaginginner walls of the rectangular housing. In this embodiment, a pair ofrectangular friction elements can be attached to opposite sides of therectangular shaft for engaging opposite inner surfaces of therectangular housing. Each rectangular friction element can also havedistinct inner and outer portions which can be made of differentcompositions and have different properties. A different means forgenerally maintaining the pressure between each friction element and thehousing within a preferred range of acceptable operating pressures isalso provided. In this case, the means can be accomplished by formingthe housing in two opposed portions, one portion can be channel shapedand the other generally flat. By sizing the channel shaped portionappropriately, shims can be used between the two opposed housingportions to provide a certain preload on the friction elements when thetwo housing portions are fastened together with the shaft and frictionelement sandwiched therebetween. The preload is calculated to take intoaccount anticipated thermal expansion of the friction elements such thatthe pressure between the friction elements and the housing does notexceed an acceptable range of operating pressures. Also, the width ofthe channel shaped member can also be sized slightly wider than thefriction elements in order to provide some space between the edges ofthe friction material and the side walls of the housing to accommodatesome amount of thermal expansion, thus reducing the buildup of pressurebetween the friction elements and the housing.

Other details, objects, and advantages of the invention will becomeapparent from the following description and the accompanying drawings ofcertain presently preferred embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawing figures certain preferred embodiments of theinvention are illustrated in which:

FIG. 1 is a perspective view of an embodiment of the invention;

FIG. 2 is a side view cross section of FIG. 1;

FIG. 3 is a side plan view of a friction element;

FIG. 4 is a section view of the friction element taken along the lineIV—IV;

FIG. 5a is a side view partially in section of an embodiment of theinvention;

FIG. 5b is an end view of FIG. 5a;

FIG. 6a is a side view partially in section of another embodiment of theinvention;

FIG. 6b is an end view of FIG. 6a;

FIG. 7a is a side view partially in section of a further embodiment ofthe invention;

FIG. 7b is an end view of FIG. 7a;

FIG. 8a is a side view partially in section of another furtherembodiment of the invention;

FIG. 8b is an end view of FIG. 8a;

FIG. 9 is a side view cross section of an embodiment of a generallyrectangular shaped friction dampener;

FIG. 10 is a cross section view taken along the line X—X in FIG. 9;

FIG. 11 is the same view as in FIG. 11 except showing a differentembodiment of the friction elements;

FIG. 12 is a side view cross section of another embodiment of agenerally rectangular shaped friction dampener;

FIG. 13 is a cross sectional view taken along line XIII—XIII in FIG. 12;and

FIG. 14 is a top plan view of one possible application of the invention.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Referring now to the drawing figures, and particularly FIGS. 1 and 2,there is shown a first embodiment of a generally cylindrical frictiondampener 10 having a tubular housing 12 slidably surrounding a tubularshaft 14. The shaft 14, or rod, can carry one or more friction elements22. The friction elements 22 frictionally engage an inside surface 16 ofthe housing 12 for controlling relative displacements between thehousing 12 and the shaft 14. The housing 12 can additionally include ameans for maintaining a peripheral pressure within a preferred range ofoperating pressures. The housing 10 preferably can have a wall 20 at anend which surrounds the shaft 14. Such a wall 20 can have an openingtherein sized to permit the shaft 14 to slide therethrough. A seal 21can also be provided between the wall 20 and the shaft 14 for keepingdirt, or water, and other foreign matter from entering inside thehousing 12 and interfering with the operation of the friction elements22 against the inside surface 16 of the housing 12. Otherwise, foreignmatter could become lodged between the friction elements 22 and thehousing 12 which can adversely affect the functioning of the frictiondampener 10 as well as cause damage to the friction elements 22 and theinside surface 16 of the housing 12. The inside surface 16 of thehousing 12 can preferably be polished and flat to provide a smooth,uniform surface for the friction elements 22 to engage.

Connecting eye members 18 and 19 can be provided at distal ends of boththe housing 12 and the shaft 14 for connecting the friction dampener 10between two independently movable elements (an example of which isillustrated in FIG. 9) that are expected to undergo relativedisplacement. The connecting eye members 18 and 19 can be, for example,spherical bearings of appropriate size and strength for the particularapplication. The shaft 14 is preferably tubular to save weight, butcould also be solid.

The friction elements 22 are preferably annular, or donut shaped asshown in FIG. 3, and have a central opening 28 through which each onecan be inserted on, and affixed to, the shaft 14. Each friction element22 can be bonded or otherwise rigidly attached to the shaft 14 such thatessentially no displacement can occur between the shaft 14 and thefriction elements 22. Each friction element 22 can be sized such thatthe outermost diameter thereof is greater than the diameter of theinside surface 16 of the housing 12 so that there is an initialperipheral pressure, selected according to the particular application,between the friction elements 22 and the housing 12. The outermostdiameter of the friction elements 22 can be chosen according to theparticular application and the desired amount of initial peripheralpressure on the housing 12.

Although two such friction elements 22 are shown in FIG. 2, more thantwo, or only one, can be used. Each friction element 22 can also have alonger or shorter axial extent to provide more or less shear force. Forexample, a shorter axial length, i.e. dimension “A” shown in FIG. 4,provides less shear force, meaning that the friction elements 22 flexless before they break lose and begin to slide on the inside surface 16of the housing 12. Conversely, a longer axial length “A” provides agreater shear force, meaning that the friction elements 22 flex more,i.e. absorb more energy, before they break lose and begin to slide alongthe inside surface 16 of the housing 12. In one preferred embodiment,wherein the desired peripheral pressure is in the neighborhood of 6,000psia, the friction elements 22 can be designed to permit about {fraction(1/16)} of an inch of displacement between the shaft 14 and the housing12 before the friction elements 22 break lose and begin to slide.

Each friction element 22 can have an inner portion 32 and an outerportion 30, as shown in FIGS. 3 and 4. The inner portion 32 canpreferably be securely affixed to the shaft 14 while the outer portion30 frictionally engages the inside surface 16 of the housing 12. Theinner portion 32 and outer portion 30 can preferably consist ofmaterials having different properties. For example, the inner portion 32can have a particular spring coefficient of compression and the outerportion 30 can have a selected friction coefficient/wear characteristic,each chosen for the particular application. For example, the innerportion 32 can be designed (taking into account the characteristics ofthe outer portion 30) to provide an initial peripheral pressure of about6,000 psia. The outer portion 30 can be of a softer or harder compounddepending on the desired friction coefficient according to theparticular application.

Referring now to FIGS. 5a -8 b, a means for maintaining the peripheralpressure between the friction elements 22 and the housing 12 within apreferred range of pressures can be achieved by configuring the housing12 in one of the ways illustrated. The particular configurations permita controlled expansion of the housing 12 in response to increasedperipheral pressure. The housing 12 can be formed in a several differentconfigurations depending upon the particular application and the desiredrange of peripheral pressure. The particular configurations permit thehousing 12 to expand in response to an increase in peripheral pressureresulting from thermal expansion of the friction elements 22. Expansionof the housing 12 can reduce the increased peripheral pressure andthereby maintain the pressure within a preferred range of pressures.

Four possible configurations, illustrated in FIGS. 5a-8 a, are shown byway of example only, and it is to be understood that otherconfigurations within the teaching of this disclosure could be providedaccomplish the same result.

In FIGS. 5a and 5 b, the housing 12 is illustrated having a cone shapedportion 34 projecting outwardly from the housing. As seen best in thecross sectional view in FIG. 5b, the cone shaped portion 34 can beintegrally formed from the sidewall of the housing 12. Upon thermalexpansion of the friction elements 22, shown in FIGS. 2-3, theperipheral pressure can cause the housing 12 to expand at the base ofthe cone shaped portion 34. The cone shaped portion 34 acts as a springso that as the peripheral pressure increases, the base of the conewidens. Thus, the cone shaped portion 34 can flex to permit the housing12 to expand in response to an increase in peripheral pressure.Consequently, the peripheral pressure can generally be maintained withina desired range of operating pressures.

In another embodiment, the housing 12 can be configured as illustratedin FIGS. 6a and 6 b, having a longitudinal split, or gap 37, along thelength thereof. A pair of side portions 38 can be integrally formed fromthe housing 12. The side portions 36 diverge from each other and projectoutwardly from the housing 12. A biasing member 38 can be provided togenerally maintain the divergent ends of the side portions 36 togetherand can help to prevent the gap 37 from overly widening, which canresult in an insufficient amount of peripheral pressure between thefriction elements 22 and the housing 12. As the friction elements 22expand and increased peripheral pressure is exerted on the housing 12,the side portions can flex to permit gap 37 to widen which reduces theperipheral pressure. Consequently, the side portions 36 and gap 37cooperated to permit the housing to expand in response to increasedperipheral pressure while the biasing member 38 simultaneously prohibitsover-expansion. Thus, the peripheral pressure can generally bemaintained within a desired range of operating pressures.

The housing 12 can also be configured as illustrated in FIGS. 7a and 7b, having a corrugated shape. In the assembled dampener 10, the frictionelements 22 generally engage the low surfaces 40, shown in FIG. 7b, ofthe corrugations. As the friction elements 22 undergo thermal expansion,the low portions 40 can deflect outwardly and reduce the peripheralpressure in a controlled manner. Thus, the housing 12 can expand toreduce the peripheral pressure and generally maintain the pressurewithin a desired range of operating pressures.

Referring now to FIGS. 8a and 8 b, a further example of how the housing12 can be configured is illustrated wherein the housing 12 is fluted.One or more flutes 42 can be provided in the housing 12 which creates anumber of flexible web portions 43. As the friction elements 22 undergothermal expansion, the web portions 43 can respond by “bowing” outwardsto reduce the pressure. Consequently, the peripheral pressure cangenerally be maintained within a desired range of operating pressures.

Referring now to FIGS. 9-12, there are shown other embodiments of afriction dampener 60, 90 according to the invention. The frictiondampeners 60, 90 shown can be similar in operation to the generallycylindrical dampener 11, except having a generally rectangular housing62 in which is slidably enclosed a generally rectangular shaft 65.Consequently, the friction elements 66, 67 are not donut shaped, butrather are rectangular. Also, it can be preferably to employ a pair ofrectangular friction elements 66, 67, attached to upper and lower sidesof the rectangular shaft 65, such that only two, opposing, sides 73, 74of the rectangular housing 62 are frictionally engaged. The upper 61 andlower 67 friction elements can be formed from the same type of materialas the annular friction elements 22. Another difference is that thehousing 62 can be adapted differently to maintain the pressure betweenthe friction elements 66, 67 and the sides 73, 74 of the housing 62within the desired range of operating pressures.

Referring to FIGS. 9-11, the generally rectangular shaft 65 carries thegenerally rectangular friction elements 66, 67 which engage innersurfaces of the housing 62. Instead of a friction element which engagesthe entire inner periphery of the housing, like the annular frictionelements 22, separate upper 66 and lower 67 rectangular frictionelements, attached to upper and lower sides of the shaft 65, can beadvantageously employed. Each friction element 66, 67 is attached to anopposite side of the shaft 65 and sandwiched between the shaft 65 andopposing inner friction surfaces 73, 74 of the rectangular housing 62.Just as with the generally cylindrical dampener 10, the upper 66 andlower 67 friction elements are attached to the shaft 65, such that thefrictional interface is between the inner friction surfaces 73, 74 ofthe rectangular housing 62 and outer, interface surfaces of the upper 66and lower 67 friction elements.

The generally rectangular housing 62 can preferably be formed from afirst member 63 and a second member 64, which are connected together,enclosing the shaft 65 and friction elements 66, 67. The first member63, as shown best in FIGS. 10 and 11, is a channel shaped member havingan upper wall 72 and sidewalls 68 and 70 extending therefrom. The innersurface 73 of the upper wall 72 is fictionally engaged by the upperfriction element 66. The second member 63 is a generally flat platemember. The inner surface 74 of the plate member 64 is the otherfriction surface of the housing 62, which is engaged by the lowerfriction element 67.

The sidewalls 68, 70 of the channel member 63 can be formed with flanges76 that extend outwardly from either side wall 68, 70. These flanges 76and can be used to connect the channel member 63 to the plate member 64.Bolts 80 can be used to fasten the channel 63 and plate 64 membertogether via aligned holes 82 provided through the plate member 64 andthe flanges 76. Depending on the length of the rectangular housing 62,multiple bolts can be employed to connect the channel 63 and plate 64members. For example, such as shown in FIGS. 9 and 12, four bolts areused on either side of the dampener 60, 90.

The friction elements 66, 67 can preferably be rigidly attached toopposite sides of the rectangular shaft 65 such that the slidingfrictional engagement occurs between the friction surfaces 73, 74 of therectangular housing 62 and outer interface surfaces of the upper 66 andlower 67 friction elements. When the shaft is 65 enclosed within therectangular housing 62, the friction elements 66, 67 can preferably besomewhat compressed between the friction surfaces 73 and 74. The channelmember 63 can be formed with a certain depth, selected such that whenthe shaft 65 carrying the friction elements 66 and 67 are disposed inthe channel and the plate member 65 is bolted to the flanges 76, thefriction elements 66 and 67 are compressed between the friction surfaces73, 74 by a predetermined amount, thereby providing an initial preload.Moreover, the amount of preload force on the friction elements 66 and 67can be adjusted using shims 78 which can be provided between the flanges76 and the plate member 64 to more closely adjust the amount of preload.The amount of preload can be, for example, in the range of about 4,000to 6,000 pounds. The amount of preload is also affected by theparticular properties of the friction element material, as will bedescribed more fully below.

As can be seen in the cross sectional views in FIGS. 10 and 11, thechannel member 63 has a width slightly larger than the width of thefriction elements 66, 67 such that there is a small amount of spaceindicated at 84 between the friction elements 66, 67 and the sidewalls68 and 70 of the channel member 63. This extra space 84 providesexpansion room to accommodate slight thermal expansion of the upper 66and lower 67 friction elements. This space 84 for thermal expansion,along with the shims 78 (for providing a certain preload on the frictionelements 66, 67) can be used to create and maintain operating conditionswherein the thermal expansion of the friction elements 66, 67 will notresult in pressures exceeding a desired range of operating pressures.

Referring particularly to FIG. 11, each of the upper 66 and lower 67friction elements may, similarly to the annular friction elements 22, beformed from inner 86 and outer 88 portions, each having differentmaterial properties. In particular, the inner portion 86, which isattached rectangular shaft 65, can be of a softer material having aselected coefficient of compression. In contrast, the outer portion 88,which frictionally engages the friction surfaces 72, 74 of therectangular housing 62, can be made from a harder material having aselected coefficient of friction. In this manner, and as explained inmore detail in connection with the description of the annular frictionelements 22, the upper 66 and lower 67 friction elements can becustomized for particular applications.

Additionally, the characteristics of the inner portion 86, taking intoaccount the characteristics of the outer portion 88, can be designedalso taking into consideration the preload amount, to provide a desiredinitial pressure against the friction surfaces 72, 74 of the rectangularhousing 62. Thus, in addition to using the shims 78, the materialproperties of the friction elements 66, 67 can be varied to tailor thefriction dampener 60, 90 to specific applications.

Where a plurality of friction elements 66, 67 are employed, such asshown in FIG. 9, the friction elements 66, 67 can have varying axiallengths depending on the application for which the dampener 60 is beingused, also as explained previously in connection with the annular shapedfriction elements 22.

An embodiment of a generally rectangular friction dampener 90 isillustrated in FIG. 12 wherein a single pair of upper 92 and lower 93friction elements are utilized. As just described, the friction elements92, 93 can have two different portions with different materialproperties, and also can have different axial lengths depending on theparticular application. In addition to the single pair of rectangularfriction elements 92, 93, the friction dampener 90 can have a bearingmember 94 attached to the distal end of the shaft 65 to provide improvedstabilization to maintain the shaft 65 in an axially aligned positionwithin the rectangular housing 62. The bearing member 94 can be madefrom an elastomeric material as well, but would not be a frictionmaterial, i.e. the bearing member 94 generally will have a relativelylow coefficient of friction. Alternatively, the bearing member 94 couldbe made from metal.

A cross section view at the bearing member 94 is shown in FIG. 13. Ascan be seen, a preferred embodiment of the bearing 94 can be arectangular member which preferably substantially fills the housing 62.The bearing member 94 should fit snugly, but not be under anycompression in the housing 62, to ensure a tight engagement so that theshaft 65 is well stabilized in an axially aligned position in thehousing 62 during operation. Since the bearing 94 material preferablyhas a low coefficient of friction, no appreciable amount of heat shouldbe generated which could cause the bearing member to expand (if madefrom an elastomer) and exert undesirable pressure on the housing 65.

A pair of friction dampeners, which can be generally cylindrical shapedfriction dampeners 10 or generally rectangular shaped friction dampeners60, 90, are shown in FIG. 14, as used in one particular application asyaw dampeners for a railway vehicle truck assembly 155, shown in phantomlines.

In operation, one friction dampener is provided on either side of thetruck assembly 155. A first end of each friction dampener is connectedto a bracket 152 on the frame portion 158 of the truck assembly 155through the connecting eye member at the distal end of the frictiondampener housing. Each connecting eye member at the distal end of eachshaft of the friction dampener is similarly connected to brackets 150which are provided on the axle portion 156 of the truck assembly 155.Each connecting eye member preferably has a spherical bearing insertdesigned to be attached to the mounting brackets 150 and 152 provided oneach of the independently movable elements 56 and 58 whose relativemovements are to be regulated by the friction dampeners. The frictiondampeners are mounted in a generally horizontal orientation so thatsubstantially all of the relative movement controlled by the dampenersis normal to the longitudinal axis of the dampener. Positioning onedampener at either side of the axis about which the opposingindependently moving elements 156 and 158 are expected to move providesbalance to the system. This configuration also permits a softer rate offriction dampener to be employed at either side of the center line ofthe truck assembly 155 which can promote a smoother, more consistentabsorption of the yaw forces resulting from the relative movements.Additionally, the provision of a friction dampener on either side of thetruck assembly 155 can reduce stress on mounting brackets 150 and 152since each bracket then only has to be strong enough to support half ofthe load compared to if only a single friction dampener is employed ononly one side of the truck assembly 155.

As the truck assembly 155 moves along the track the axle portion 156 isexpected to undergo movements about an axis denoted by reference numeral160 relative to the frame portion 158 of the truck assembly 155. As theaxle portion 156 undergoes these movements, the shaft of each of thefriction dampeners will be moved relative to the housing. As the axleportion 156 rotates about the axis 160, the shaft of one of the frictiondampeners is forced into the housing while the shaft of the opposingfriction dampener is drawn out from the housing. In both the compressionstroke (shaft pushed into housing) and the extension stroke (shaft drawnout from housing) the friction elements engage the friction surface(s)of the housing to dampen the movements. This type of operation isreferred to as two-way operation, which means that the frictiondampeners absorb energy both as the shaft is being pushed into and drawnout from the housing.

Due to the large amount of weight transported on the railway vehicletruck assemblies 155, a great deal of heat can be generated as thefriction elements engage the friction surface(s) of the housing. Some ofthis heat is transferred into the atmosphere through the housing, butmost is absorbed by the friction elements. The elastomeric materialwhich the friction elements are formed of can be significantly affectedby temperature. Typically, the elastomeric material expands and thefriction coefficient changes. The expansion rate and the amount ofchange in the friction coefficient can vary depending on the particularcompound used. This condition is best understood by analogy to the tireson a racing car. Race car drivers often spin the tires to heat up therubber so that the tires become “tacky” and can stick to the track.Also, as the air in the tires heats up its causes the tires to expand.The tackier tires and the larger, expanded diameter both serve to helpthe car achieve higher speeds. The elastomeric material is similar thetires on the race car in that as they get warmer they both expand andmore strongly adhere to the friction surface(s) in the housing. Theresult is that as the temperature increases the engagement between thefriction elements and the friction surface(s) in the housing canincrease to the point where a great deal more force is required to causethe friction elements to slide within the housing. Although desirablefor the race car driver, this condition can be disastrous in the case ofa friction dampener. Unlike the tires and the track, it is generallydesirable that the friction dampener maintain a relatively constantfriction coefficient between the friction elements and the frictionsurface(s) in the housing. To accomplish this it can be very importantto maintain the pressure between the friction elements and the frictionsurface(s) in the housing within a preferred range of operatingpressures.

If no means for maintaining the peripheral pressure within a certainrange of acceptable operating pressures is provided, the increasedpressure and higher friction coefficient can cause the friction dampenerto reach a point where virtually no relative displacement between theshaft and the housing can occur. In effect, the friction dampener canbegin to behave like a fixed rod. This is a very undesirable conditionwhich can cause damage to the dampener and result in an unsafe conditionin the railway vehicle truck assembly 155. The inability to dampen theyaw forces of the truck assembly 155 can result in an uncontrolledhunting condition which, in a worst case, can result in derailment.Consequently, the friction dampeners, both of the cylindrical andrectangular embodiment, each employ some manner, as described in detailabove, of maintaining the pressure between the friction elements and thefriction surface(s) within a desired operating range, as describedabove.

Particularly in regard to the elastomeric material from which thefriction elements are formed, the preferred composition can varydepending on the particular application and the corresponding materialproperties desired. Suitable elastomeric materials can be purchased fromC.U.E., having a place of business in Butler County, Pa. With respect tocertain desirable properties of the elastomeric material, some examples,and a discussion of such elastomers used in the context of railcar truckassemblies is provided in my U.S. Pats. Ser. Nos. 3,957,318 and4,080,016, both of which are hereby incorporated herein by reference.

Although certain embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodification to those details could be developed in light of the overallteaching of the disclosure. Accordingly, the particular embodimentsdisclosed herein are intended to be illustrative only and not limitingto the scope of the invention which should be awarded the full breadthof the following claims and any and all embodiments thereof.

What is claimed is:
 1. A friction dampener for interposition betweenseparate independently movable elements which are expected to undergorelative displacements, said friction dampener comprising: a. a housinghaving a first connecting member for connection to a first independentlymovable element; b. a shaft having a first end slidably disposed in saidhousing and an opposite end having a second connecting member forconnection to a second independently movable element; c. at least onefriction element carried by said shaft in contact with and frictionallyengaging said housing; and d. said housing configured to accommodatethermal expansion of said at least one friction element without aresulting increase in pressure between said at least one frictionelement and said housing; and e. wherein said at least one frictionelement frictionally engages less than an entire perimeter of saidhousing to provide space for said at least one friction element toexpand such that pressure between said at least one friction element andsaid housing does not increase to permit said pressure to be generallymaintained within a range of desired pressures.
 2. The friction dampenerof claim 1 wherein said housing, said shaft and said friction elementsare generally rectangular shaped.
 3. The friction dampener of claim 1wherein said at least one friction element is at least two frictionelements attached to said shaft at spaced apart locations.
 4. Thefriction dampener of claim 3 wherein each of said at least two frictionelements is a pair of friction elements, each of said pair of frictionelements attached to opposite sides of said rectangular shaft at saidspaced apart locations.
 5. The friction dampener of claim 1 furthercomprising: a. said housing having a generally rectangular shape definedby a pair of opposed friction surfaces and a pair of opposed side walls;b. said at least one friction element having at least one interfacesurface engaging at least one of said pair of opposed friction surfacesof said housing, said interface surface having a width less than thespace between said pair of opposed side walls; and c. said housing atleast partially accommodating thermal expansion of said at least onefriction element between said opposed side walls such that pressurebetween said at least one friction element and said housing resultingfrom anticipated thermal expansion of said at least one friction elementis generally maintained within said range of desired pressures.
 6. Thefriction dampener of claim 5 wherein said at least one friction elementis at least two friction elements attached to said shaft at spaced apartlocations.
 7. The friction dampener of claim 5 further comprising: a.said shaft having a generally rectangular shape; b. said at least onefriction element is at least two friction elements attached to saidrectangular shaft at the same location on opposite sides of said shaft;and c. said at least one interface surface of each of said at least twofriction elements engaging respective ones of said pair of opposedfriction surfaces of said housing.